The present invention relates to an electrodeless lamp, that is to say a hollow structure containing a material excitable by radio frequency energy to emit visible light.
It is known to fabricate such lamp from sintered ceramic components. For instance, U.S. Pat. No. 5,727,975 describes the production of lamps from components that are shrunk fitted to each other.
The object of the present invention is to enable an electrodeless lamp to be constructed from components which are sealed together using a glass or alumina frit have a melting temperature higher than that of a charge of excitable material in the lamp.
According to a first aspect of the invention there is provided an electrodeless lamp comprising:
a hollow body of ceramic material having an open end and containing a charge of excitable material with a given melting point;
a translucent closure at the open end of the body;
a seal between the body and the closure, the seal being of fused material having a fusing point higher than that of the excitable material.
According to another aspect of the invention there is provided a method of production of an electrodeless lamp of the first aspect, the method consisting in the steps of:
applying frit material to the open end of the hollow body prior to sealing;
inserting the charge of excitable material into the hollow body;
positioning the translucent closure across the open end of the hollow body;
applying laser irradiation to the frit material through the translucent closure, to locally raise its temperature to its fusing point for sealing of the window to the body without causing the excitable material to melt.
The laser may be traversed around the periphery of the body at its open end, to fuse the window to the body with the frit around the entire periphery. Alternatively, the laser may be arranged to provide an annular irradiation of the window around the entire periphery simultaneously.
Preferably, the irradiation will be carried out in a chamber, where the body and the window have been preheated at high vacuum to draw any volatile material from these components prior to sealing. Conveniently, the window is arranged at, but not across, the end of the body during the pre-heat and evacuation. The excitable material is then introduced into the body, the window moved into position and the laser operated to effect the seal.
Whilst the lamps can be processed individually in the chamber, it is preferred to process a plurality of them, mounted in a jig, in the chamber at one time.